Correction method for chip removal machines

ABSTRACT

The invention concerns a method for determining a deviation of at least one regulating variable on chip removal machines with a mechanical drive for a tool and/or a workpiece, regulated by a control system, wherein the regulation comprises a plurality of values C, X, Z of at least three spatial axes c, x, z for the control system and for the drive, and the values C, X, Z have a functional relation such as Z=f bi  (C, X) with the axes c, x, z. A protocol is prepared from a plurality of control system actual values (C p,s , X p,s , Z p,s ) detected by measuring means and/or selected drive actual values (C p,a , X p,a , Z p,a ) and a control system nominal value according to Z bi,s =f bi  (C p,s , X p,s ) and/or a drive nominal value according to Z bi,a =f bi  (C p,a , X p,a ) is calculated at least in relation to the z-axis, and a control system differential value according to D z,s =Z p,s −Z bi,s  and/or a drive differential value according to D z,a =Z p,a −Z bi,a  is calculated at least in relation to the z-axis. The invention also pertains to a chip removal machine which implements such a method.

FIELD OF THE INVENTION

The invention concerns a method for determining a deviation of at leastone regulating variable on chip removal machines with a mechanical drivefor a tool and/or a workpiece, regulated by a control system, whereinthe regulation comprises a plurality of values C, X, Z of at least threespatial axes c, x, z for the control system and for the drive, and thevalues C, X, Z have a functional relation such as Z=f_(bi) (C, X) withthe axes c, x, z.

BACKGROUND OF THE INVENTION

It is already generally known, especially for production processes inprogress, how to compare the nominal values which are preset orcalculated by a control system to the actual values of the tool so as toperform an adjustment of the actual values. Such is also described by CH425 958. In highly dynamic processes with several functionallyinterrelated axes, however, this regulating procedure is not applicable,since for example it takes around four working and computing clockperiods from the time the control system sends the nominal value to thedrive, until the actual positioning of the drive occurs. As a rule,furthermore, the control system produces a separate pilot value, whichinfluences the settings of the drive or the control current of the drivein the desired manner. Thus, the nominal values and the respectiveactual values can no longer be matched up and compared.

Thus far, the work piece after being manufactured has been optically ormechanically measured, thus drawing a conclusion as to any deviationsduring the manufacturing process.

WO 02/37168 A describes a method for controlling a 4-axis (Z, Z′, C, X)chip removal machine, in which a functional relation of the form Z=f(C,X) exists. It describes a “feedforward” control system which does notenvision the differential value of the invention.

SUMMARY OF THE INVENTION

The basic aim of the invention is to configure and arrange a machiningprocess such that an optimal representation of the deviation between thenominal value and the actually generated workpiece value is assured.

This aim is achieved, according to the invention, in that a protocol isprepared from a plurality of control system actual values (C_(p,s),X_(p,s), Z_(p,s)) detected by measuring means and/or selected driveactual values (C_(p,a), X_(p,a), Z_(p,a),), and a control system nominalvalue according to Z_(bi,s)=f_(bi) (C_(p,s), X_(p,s)) and/or a drivenominal value according to Z_(bi,a)=f_(bi) (C_(p,a), X_(p,a)) iscalculated at least in relation to the z-axis, and a control systemdifferential value according to D_(z,a)=Z_(p,s)−Z_(bi,s) and/or a drivedifferential value according to D_(z,a)=Z_(p,a)−Z_(bi,a) is calculatedat least in relation to the z-axis. A similar situation is provided forthe c-axis and the x-axis. It should be noted that the nominal value,such as Z_(bi,a), is calculated by using the respective protocol value,i.e., the actual value, such as C_(p,a) and X_(p,a).

As a result, the actual value of one axis is compared with thecalculated nominal value of this axis on the basis of the actual valuesof the other axes, taking into consideration their functional relationf_(bi).

This actual value comes very close to the physical value such as mightbe ascertained only individually by a subsequent measurement technique,for example, by mechanical sensing, or by an optical measurement methodlike a hologram. But the small number of measured points duringmechanical sensing does not let one evaluate minor errors, such as thosecaused by the static friction of a defective axial bearing of themachine, since no such resolution is possible.

Moreover, the optical measurement technique is extremely time-consumingand tedious, so that the number of different workpieces or the variationin production is very limited.

Provision is made so that at least one spatial axis can be configured asa translatory spatial axis x, z and at least one spatial axis as arotary spatial axis c.

For this, it is also advantageous to determine, at least for the driveand the z-axis, a contouring differential value according to D_(z,a)^(φ)=Z_(p,a)−Z_(bi,a) ^(φ) with Z_(bi,a) ^(φ)=f_(bi) (C_(p,a)+Δφ,X_(p,a)), where the value Δφ corresponds to a phase shift of the c-axis.Thus, the influence of a continuous or constant phase shift Δφ of thec-axis is left out of consideration when assessing the quality of thecutting process. This phase shift Δφ after all results merely in atorsion of the generated lens contour starting from a theoreticalinitial position, and the torsion can be equalized by a correction ofthe mounting position of the lens thus produced.

An additional possibility, according to a further modification, is thatthe phase shift Δφ is between 0.5° and 3°, especially 1.0°, and thedetermination of Z_(bi,a) ^(φ) is done between +Δφ and −Δφ with anincrement between 0.05° and 0.2°, especially 0.1°. This provides asufficient resolution for identification of a contouring error.

Moreover, it is advantageous to compute, at least from the differentialvalues D_(z,s), D_(z,a) and/or the contouring differential valuesD_(z,a) ^(φ) at least for the z-axis, one peak-to-valley value for thecontrol system according to D_(z,s,ptv)=D_(z,s,max)−D_(z,s,min) and forthe drive according to D_(z,a,ptv)=D_(z,a,max)−D_(z,a,min), D_(z,a) ^(φ)_(ptv)=D_(z,a,max) ^(φ−D) _(z,a,min) ^(φ), where D_(z,s/a,min)corresponds to the minimum and D_(z,s/a,max) to the maximum differentialvalue of the respective measurement and D_(z,a,max) ^(φ), D_(z,a,min)^(φ) corresponds to the respective position of the c-axis, taking intoaccount ±Δφ. Similar provision is also made for the other axes.

It is also advantageous to determine an error differential valueaccording to D_(z,a) ^(f=Z) _(p,a)−Z_(bi,a) ^(f) with Z_(bi,a)^(f)=f_(bi) (C_(p,s), X_(p,s)) at least for the drive and at least inrelation to the z-axis. The error differential value D_(z,a) ^(f) is ameasure of the deviation of the respective cutting process, and it alsomakes it possible to identify other factors of influence of the machine,such as bearing fault. Similar provision is also made for the controlsystem and the other axes.

Provision is made for the function f_(bi) to be a 3D bicubic surfacespline and/or spiral spline. Thanks to the polynomial coefficients whichare known at each lattice point of the surface spline, any given pointin the lattice of the surface spline can be computed.

The spiral spline is computed in terms of the polynomial coefficients,starting at different lattice points of the surface spline.

It is of significance to the invention that the differential valuesD_(z,a), D_(z,s), the contouring differential values D_(z,a) ^(φ), therespective peak-to-valley values D_(z,a,ptv), D_(z,s,ptv), D_(z,a) ^(φ)_(ptv) and/or the actual value Z_(p,s), Z_(p,a) of at least the z-axisare represented, and at least the representation of D_(z,a,ptv),D_(z,s,ptv), and/or D_(z,a) ^(φ) _(ptv) is done with the smallestpossible peak-to-valley value. The other measurement values, which arebased on a different phase shift Δφ or a different contouring error ofthe c-axis, are disregarded, as mentioned above. This phase shift Δφ canbe taken into account through the mounting position. Similar provisionis also made for the control system and the other respective axes.

In conjunction with the configuration and arrangement of the invention,it is advantageous to represent the size and/or the deviation of atleast the peak-to-valley value D_(z,s,ptv), D_(z,a,ptv), D_(z,a) ^(φ)_(ptv) and/or the actual value Z_(p,s), Z_(p,a) in terms of therespective workpiece position. This representation can be done by acontour line and/or a contour spiral, specifying the angle and theradius.

Moreover, it is advantageous to distinguish optically between negativeand positive values and/or optically in terms of the magnitude of thevalues when representing the differential value and/or the contouringdifferential value D_(z,a), D_(z,s), D_(z,a) ^(φ). It is especiallyadvantageous to use optically graduated intensity levels for positiveand/or negative differential values and/or contouring differential valueD_(z,a), D_(z,s), D_(z,a) ^(φ) with different color tones in terms oftheir magnitude. Positive differential values and/or the contouringdifferential value D_(z,a), D_(z,s), D_(z,a) ^(φ) could be graduatedfrom yellow to red according to their magnitude, for example, andnegative differential values and/or the contouring differential valueD_(z,a), D_(z,s), D_(z,a) ^(φ) from green to blue according to theirmagnitude. Other color grades are also envisioned. In addition, agraduation in terms of different samples in the manner of the sampleembodiment is provided.

Moreover, it is advantageous to provide a superimposed representation ofthe differential value and/or the contouring differential value D_(z,a),D_(z,s), D_(z,a) ^(φ) and the actual value Z_(p,s), Z_(p,a), therespective scale being different for the two values. Whereas theabsolute actual value Z_(p,s), Z_(p,a) varies in the range of a fewmillimeters, the differential values D_(z,a), D_(z,s), D_(z,a) ^(φ) arein micrometers, i.e., lower by a factor of 1000. The representation inFIG. 2 is nevertheless informative.

Furthermore, it is advantageous to calculate, for one or more other axesx, c, the nominal values C_(bi), X_(bi), the differential valuesD_(x/c,a), D_(x/c,s), the peak-to-valley value D_(x/c,a,ptv), D_(x/c,a)^(φ) _(ptv), D_(x/c,s,ptv), D_(x/c,s) ^(φ) _(ptv), the errordifferential value D_(x/c,a) ^(f), D_(x/c,s) ^(f) and/or the contouringdifferential value D_(x/c,s) ^(φ), D_(x/c,a) ^(φ) for the control systemand/or for the drive. This makes possible a comprehensive evaluation ofthe cutting process outcome.

Finally, it is advantageous to provide for a correction cut, in additionto a main cut and an optional precision cut during the chip removalmachining of the workpiece, at least making use of the differentialvalues D_(z,a), D_(z,s), D_(z,a) ^(φ). Besides the possibility of usingthe above-described method for adjusting the various parameters of thechip removal or cutting machine, one can provide for an additionalcorrection cut after a main cut, which generally constitutes the end ofthe cutting machining. The correction cut can then retroactively machineat least the positive deviations of the workpiece.

For this, it is also especially advantageous to use the above-mentionedmethod for a chip removal machine for the production of optical lensesfrom plastic.

Finally, it is advantageous to convert the values C, X, Z of the axes c,x, z into the Cartesian system of coordinates or into the polar systemof coordinates. Switching between the different coordinate systemsallows one to handle the most varied customer and manufacturer data.

In this case, it is advantageous to start from a theoretical cuttingpoint of an ideal point-like tool and convert the values C, X, Z of theaxes c, x, z for use of a circular carbide tip, with the circularcarbide tip having a center point corresponding to the theoreticalcutting point. This so-called off-set data constitutes the basis for theabove-mentioned surface spline, which thereby determines the off-setsurface serving as the basis for the spiral spline.

It is advantageous to use at least one differential value D_(z,a) and/orone contouring differential value D_(z,a) ^(φ) as an exclusion criterionfor the control system's actual values (C_(p,s), X_(p,s), Z_(p,s))and/or as an adjustment criterion for the various machine parameters andthe machine's control system.

The invention also pertains to a chip removal machine with a mechanicaldrive for a tool and/or a workpiece, regulated by a control system,wherein the regulation comprises a plurality of values C, X, Z of atleast three spatial axes c, x, z for the control system and for thedrive, and the above-described method is used for determining thedeviation of the regulating variables.

It is advantageous to provide an output unit for the representation ofthe above-described values, especially the differential values D_(z,a)and/or the contouring differential value D_(z,a) ^(φ).

BRIEF DESCRIPTION OF THE DRAWINGS

Additional benefits and details of the invention are discussed in thepatent claims and in the specification, and presented in the figures.These show:

FIG. 1, a representation of the differential values of a lens surface;

FIG. 2, the representation of the z-value with the representation of thecorresponding differential value.

DETAILED DESCRIPTION OF THE INVENTION

A workpiece or optical lens 1 depicted in FIG. 1 has an actual surfacethat deviates from the nominal surface and thus contains an error.

Given a nominal surface, not shown here, the surface depicted here hasvarious regions 2.1-2.3,

3.1-3.3, in which the actual value differs from the theoretical nominalvalue. The regions indicated by 2.1-2.3, i.e., the dotted surfaces, arepositive deviations 2 from the nominal value, and the regions 3.1-3.3,i.e., the checkered regions, are negative deviations 3 from the nominalvalue.

Besides the fundamental distinction between positive 2.1-2.3 andnegative 3.1-3.3 deviations, i.e., positive and negative differentialvalues, the respective differential values are also graduated bymagnitude. Thus, as regards the positive differential values, inaddition to the regions with a deviation of 1^(st) degree (2.1) thereare also regions with a deviation of 2^(nd) degree (2.2) and 3^(rd)degree (2.3). The various degrees of graduation in this method ofrepresentation with essentially separate and different samples involvedifferent regions of deviation values, which are assigned at leastoptically to the respective degree of deviation. In the case of a colorgradation, not represented here, the different degrees of deviation areless digitized or pass smoothly into each other.

In corresponding fashion, for the negative differential values, showncheckered, there are likewise regions with deviations of 1^(st) degree(3.1), deviations of 2^(nd) degree (3.2) and deviations of 3^(rd) degree(3.3).

In a sample embodiment, not shown, provision is also made to have otherdigitized degrees of deviation besides these degrees of deviation,thereby ensuring a higher resolution for this differential valuestructure.

The diagram presented in FIG. 2 shows the z-value 4 of the lens 1depicted in FIG. 1, first absolutely (top diagram) and secondly therespective differential value relative to the nominal value (bottom).There is a different scale used in the two representations, due to thevery different size of the z-value 4 and of the differential value interms of magnitude. The z-value 4 shown here is based on an outer radiusof 30.621 mm, i.e., near the margin of the lens with a diameter ofaround 60 mm. Based on a starting value of 0.0, corresponding to theunmachined blank, the actual z-value 4 depicted here travels in a regionbetween 3.723 mm and 5.194 mm beneath the former 0-level. Thecorresponding differential value, i.e., the deviation value of thedepicted actual z-value 4, ranges between 7.9 μm above and 7.8 μm belowthe nominal z-value 4. In a sample embodiment, not shown, a superimposedrepresentation is provided for the two values, at least for a partialregion and with sufficient scale.

1. A method for determining a deviation of at least one regulatingvariable on a chip removal machine with a mechanical drive for a tool ora workpiece or a combination thereof, regulated by a control system,wherein the regulation comprises a plurality of values C, X, Z of atleast three spatial axes c, x, z for the control system and for thedrive, and the values C, X, Z have a functional relation f_(bi) such asZ=f_(bi) (C, X) with the axes c, x, z, comprising the steps of: a)preparing a protocol from a plurality of control system actual values(C_(p,s), X_(p,s), Z_(p,s)) detected by measuring means or selecteddrive actual values (C_(p,a), X_(p,a), Z_(p,a)) or combinations thereof,b) calculating a control system nominal value according toZ_(bi,s)=f_(bi) (C_(p,s), X_(p,s)) or a drive nominal value according toZ_(bi,a)=f_(bi) (C_(p,a), X_(p,a)) or a combination thereof at least inrelation to the z-axis, and c) calculating a control system differentialvalue according to D_(z,s)=Z_(p,s)−Z_(bi,s) or a drive differentialvalue according to D_(z,a)=Z_(p,a)−Z_(bi,a) or combinations thereof atleast in relation to the z-axis.
 2. The method according to claim 1,wherein at least for the drive and the z-axis a contouring differentialvalue is determined according toD _(z,a) ^(φ) =Z _(p,a) −Z _(bi,a) ^(φ)withZ _(bi,a) ^(φ) =f _(bi)(C _(p,a) +Δφ, X _(p,a)), where the value Δφcorresponds to a phase shift of the c-axis, which results in a torsionof the generated lens contour.
 3. The method according to claim 2,wherein the phase shift Δφ is between 0.5° and 3°, and the determinationof Z_(bi,a) ^(φ) is done between +Δφ and −Δφ with an increment between0.05° and 0.2°.
 4. The method according to claim 2, wherein onecomputes, at least from the differential values D_(z,s), D_(z,a) or thecontouring differential values D_(z,a) ^(φ) or a combination thereof atleast for the z-axis, one peak-to-valley value for the control systemaccording toD _(z,s,ptv) =D _(z,s,max) −D _(z,s,min) and for the drive according toD _(z,a,ptv) =D _(z,a,max) −D _(z,a,min),D _(z,a) ^(φ) _(ptv) =D _(z,a,max) ^(φ) −D _(z,a,min) ^(φ), whereD_(z,s/a,min) corresponds to the minimum and D_(z,s/a,max) to themaximum differential value of the respective measurement and D_(z,a,max)^(φ), D_(z,a,min) ^(φ) corresponds to the respective position φ, +Δφ and−Δφ of the c-axis, taking into account ±Δφ.
 5. The method according toclaim 1, wherein one determines an error differential value according toD _(z,a) ^(f) =Z _(p,a) −Z _(bi,a) ^(f)withZ _(bi,a) ^(f) =f _(bi)(C _(p,s) , X _(p,s)) at least for the drive andat least in relation to the z-axis.
 6. The method according to claim 1,wherein the function f_(bi) is a 3D bicubic surface spline or a spiralspline or a combination thereof.
 7. The method according to claim 4,wherein the differential values D_(z,a), D_(z,s), the contouringdifferential values D_(z,a) ^(φ), the respective peak-to-valley valuesD_(z,s,ptv), D_(z,a,ptv), D_(z,a) ^(φ) _(ptv) or the actual valueZ_(p,s), Z_(p,a) of at least the z-axis or combinations thereof arerepresented, and at least the representation of D_(z,s,ptv),D_(z,a,ptv), and/or D_(z,a) ^(φ) _(ptv) is done with the smallestpossible peak-to-valley value.
 8. The method according to claim 4,wherein the size or the deviation or a combination thereof of at leastthe peak-to-valley value D_(z,s,ptv), D_(z,a,ptv), D_(z,a) ^(φ) _(ptv)or the actual value Z_(p,s), Z_(p,a) or a combination thereof isrepresented in terms of the respective workpiece position.
 9. The methodaccording to claim 7, wherein one distinguishes optically betweennegative and positive values when representing the differential value orthe contouring differential value D_(z,a), D_(z,s), D_(z,a) ^(φ) oroptically in terms of the magnitude of the values or combinationsthereof.
 10. The method according to claim 7, wherein positive ornegative or a combination thereof differential values or contouringdifferential values D_(z,a), D_(z,s), D_(z,a) ^(φ) or a combinationthereof are optically graduated by different color tones in terms oftheir magnitude or by different color tone intensities in terms of themagnitude of the values or a combination thereof.
 11. The methodaccording to claim 7, wherein one provides for a superimposedrepresentation of the differential value and/or the contouringdifferential value D_(z,a), D_(z,s), D_(z,a) ^(φ) and the actual valueZ_(p,s), Z_(p,a), the respective scale being different for the twovalues.
 12. The method according to claim 1, wherein one calculates, forone or more other axes x, c, the nominal values C_(bi), X_(bi), thedifferential values D_(x/c,a), D_(x/c,s), the peak-to-valley valueD_(x/c,a,ptv), D_(x/c,a) ^(φ) _(ptv), D_(x/c,s,ptv), D_(x/c,s) ^(φ)_(ptv), the error differential value D_(x/c,a) ^(f), D_(x/c,s) ^(f)and/or the contouring differential value D_(x/c,s) ^(φ), D_(x/c,a) ^(φ)or a combination thereof for the control system or for the drive or acombination thereof.
 13. The method according to claim 2, wherein oneprovides for a correction cut, in addition to a main cut and an optionalprecision cut during the chip removal machining of the workpiece, atleast making use of the differential values D_(z,a), D_(z,s), D_(z,a)^(φ).
 14. The method for a chip removal machine for the production ofoptical lenses from plastic according to claim
 1. 15. The methodaccording to claim 1, wherein one converts the values C, X, Z of theaxes c, x, z into the Cartesian system of coordinates or into the polarsystem of coordinates.
 16. The method according to claim 1, wherein onestarts from a theoretical cutting point of an ideal point-like tool andconvert the values C, X, Z of the axes c, x, z for use of a circularcarbide tip, with the circular carbide tip having a center pointcorresponding to the theoretical cutting point.
 17. The method accordingto claim 2, wherein one uses at least one differential value D_(z,a) orone contouring differential value D_(z,a) ^(φ) or a combination thereofas an exclusion criterion for the control system's actual values(C_(p,s), X_(p,s), Z_(p,s)) or as an adjustment criterion or acombination thereof for the various machine parameters and the machine'scontrol system.
 18. A chip removal machine comprising: a mechanicaldrive for a tool or a workpiece or a combination thereof, regulated by acontrol system, wherein the regulation comprises a plurality of valuesC, X, Z of at least three spatial axes c, x, z for the control systemand for the drive, wherein the values C, X, Z have a functional relationf_(bi) such as Z=f_(bi) (C, X) with the axes c, x, z, wherein a methodis used to determine the deviation of the regulating variables, andwherein the method comprises the steps of a) preparing a protocol from aplurality of control system actual values (C_(p,s), X_(p,s), Z_(p,s))detected by measuring means or selected drive actual values (C_(p,a),X_(p,a), Z_(p,a)) or a combination thereof, b) calculating a controlsystem nominal value according to Z_(bi,s)=f_(bi) (C_(p,s), X_(p,s)) ora drive nominal value according to Z_(bi,a)=f_(bi) (C_(p,a), X_(p,a)) ora combination thereof at least in relation to the z-axis, and c)calculating a control system differential value according toD_(z,s)=Z_(p,s)−Z_(bi,s) or a drive differential value according toD_(z,a)=Z_(p,a)−Z_(bi,a) or combinations thereof at least in relation tothe z-axis.
 19. The chip removal machine according to claim 17, whereinan output unit is provided for the representation of the values, andwherein the function f_(bi) is a 3D bicubic surface spline or a spiralspline or a combination thereof.